Riot Web is a browser based user interface for the Matrix federated communications system. It allows you to do encrypted one-to-one or group chat, and has some fancy WebRTC features for voice and video conversations. The WebRTC stuff won't work in a Tor browser though. This type of system is fine for general public communications and collaboration on open source projects or gaming groups. For things which require real privacy though stick to XMPP with OMEMO.
Log into your system with:
ssh myusername@mydomain -p 2222
Using cursor keys, space bar and Enter key select Administrator controls and type in your password.
Select Add/Remove Apps then riot and also make sure that matrix is selected or was previously installed. You will then be asked for a domain name and if you are using FreeDNS also the code for the domain which can be found under Dynamic DNS on the FreeDNS site (the random string from "quick cron example" which appears after update.php? and before >>). For more details on obtaining a domain and making it accessible via dynamic DNS see the FAQ. Typically the domain name you use will be a subdomain, such as riot.mydomainname.net. It will need to be a domain which you have bought somewhere and own and not one of the FreeDNS subdomains, otherwise you won't be able to get a SSL/TLS certificate for it.
Go to the Administrator control panel and select Passwords then matrix. This will give you the password to initially log in using the Riot Web user interface. Log in, and that's it. Happy chatting.